1. Technical Field
The invention disclosed broadly relates to line terminators for communication buses and more particularly relates to compensated line termination for communication buses meeting military standard specifications.
2. Background Art
In digital communications systems, more than one device driver can be asserting the bus at any given time. This causes the termination current to the line to be shared by one or more device drivers. If one device driver releases a line while another remains on, a current pulse is sent on the line. The on driver eventually sinks the additional current, but as a result, a current pulse is produced. As a result of the current pulse, a voltage pulse or wired-OR-glitch (WOG) develops. This glitch can cross a receiver threshold and change the digital signal on the bus from a zero to a one or vice-versa.
In the military avionics communications systems employing PIBUS or in the commercial setting, Futurebus, the voltage of the WOG can be significantly different over the specified operational temperature range. To receive valid data, the bus cannot be interrogated until the WOG dissipates. In a high speed data communications system, this time can be significantly long on the order of 20 or more nanoseconds. This severely limits the data transfer rate of the communications system.
The PIBUS or Futurebus has a standard requiring a two volt supply on the termination resistance. This two volt supply is an extra supply that must be provided to drive the communication bus interface modules and must deliver somewhere in the neighborhood of 20-40 amps. This supply takes up weight, space and reduces the overall efficiency of the system. Where space, weight and efficiency are important, such as in military and commercial aircraft, such a power supply is expensive in terms of cost, weight, reliability and maintenance.